Variability in microleakage observed in a total-etch wet-bonding technique under different handling conditions

Bonding of all-porcelain crowns: structural characteristics of the substrate

OBJECTIVES

The aim of this in vitro study was to evaluate the morphology of dentin in teeth prepared for single-unit all-porcelain crowns (SUAPC) in terms of tubule orientation, density and increase in surface area after etching.

METHODS

Twenty anterior and 20 posterior teeth from adults were prepared 1mm below the cemento-enamel junction (CEJ) for SUAPC. The samples were divided into groups based on type of tooth (anterior or posterior) and bonding system employed. The teeth were processed for evaluation of morphology of the substrate, hybrid layer thickness and resin tag formation. The observations were subdivided according to location in the preparation and tubule density was calculated.

RESULTS

The observations revealed the variability in tubule density and orientation in different areas within any one preparation. The morphology of the cervical margin was less predictable with the presence of cementum and an ill-defined cemento-dentinal junction. Statistically significant differences in the density of tubules were found depending on location. Groups 2, 3, 5 and 6 samples showed that the hybrid layer thickness and resin tag morphology depended on the density and direction of tubules. In those sectors with parallel and oblique tubule orientation and with a low density of tubules, the hybrid layer was significantly thinner than in areas with cross-sectioned tubules.

SIGNIFICANCE

The cementum and the peripheral intertubular dentin surface area are likely to be responsible for the bond strength after acid etching of crown preparations, but not all areas exhibited equal responses to etching. In particular, the bonding substrate at the gingival margins may contribute little in terms of micromechanical retention.

Association between microtensile bond strength and leakage in the indirect resin composite/dentin adhesively bonded joint

PURPOSE

Develop a methodology to correlate microtensile bond strength (microTBS) and leakage within the same site of a specimen and evaluate the predominate debond and leakage pathways.

MATERIALS AND METHODS

A Class II (MO) slot cavity was prepared in 37 extracted human molars and restored with indirect resin composite restorations. The restored teeth were thermocycled 300X between 5 and 55 degrees C and then stained with silver. Two specimens per tooth were obtained by diamond saw sectioning for measurement of leakage (microm) and microtensile bond strength (MPa) at the gingival wall and then tested for association with regression analysis. Scanning electron microscopy techniques and energy dispersive spectroscopy (EDS) were used to evaluate the debond and leakage pathways.

RESULTS

Association between leakage and bond strength was not significant (t=1.31, p=0.198). All 74 samples debonded within the joint, predominantly at the hybrid layer-adhesive resin region with only one specimen including a small portion of resin cement in the debond pathway. Secondary and backscatter imaging and EDS analysis showed leakage in all samples that involved the hybrid layer.

CONCLUSION

This study demonstrates a feasible method for evaluating leakage and bond strength at the joint interface within the same specimen.

Bond strength of composite to dentin using conventional, one-step, and self-etching adhesive systems

OBJECTIVES

This in vitro study compared the dentin bonding performance of eight adhesive systems using a microtensile bond strength test.

METHODS

Thirty bovine teeth were ground to 600-grit to obtain flat root-dentin surfaces. Two conventional adhesive systems (Scotchbond Multipurpose Plus, OptiBond FL), four one-step adhesive systems (Scotchbond 1, Asba S.A.C., Prime and Bond NT, Excite) and two self-etching adhesive materials (Clearfil Liner Bond 2 V and Prompt L-Pop) were evaluated. Each bonding system was applied according to manufacturer's instructions and followed by composite (Z100) application. Immediately after bonding, the teeth were prepared for microtensile testing. Bond strength to dentin was measured using a Vitrodyne V-1000 universal tester. There were 14 replicates for each material. Fractured specimens were further observed by SEM.

RESULTS

Scotchbond Multipurpose Plus exhibited significantly (p<0.05) higher bond strength values (30.3+/-9.4 MPa) than all other materials. The bond strengths of the other materials were (from highest to lowest): Opitbond FL (22.4+/-4.3 MPa); Scotchbond 1(18.9+/-3.2); Clearfil Liner Bond 2 V (18.9+/-3.0); Prime and Bond NT (18.3+/-6.9); Asba S.A.C. (14.4+/-2.9); Excite (13.8+/-3.7); and Prompt L-Pop (9.1+/-3.3). Statistical comparisons frequently overlapped, but Optibond was significantly (p<0.05) greater than Asba, Excite, and Prompt L-Pop; whereas, Scotchbond 1 was only significantly (p<0.05) greater than Prompt L-Pop. Asba, Excite and Prompt L-Pop were not significantly different. The fracture modes were mostly adhesive.

CONCLUSIONS

The conventional adhesive systems produced higher bond strengths to root dentin than most one-step adhesives and one self-etching adhesive; with the exception of one material in each respective system.

Polymerization Contraction Stress of Resin Composite Restorations in a Model Class I Cavity Configuration Using Photoelastic Analysis

PURPOSE

An important factor that contributes to deterioration of resin composite restorations is contraction stress that occurs during polymerization. The purpose of this article is to familiarize the clinician with the characteristics of contraction stress by visualizing the stresses associated with this invisible and complex phenomenon.

MATERIALS AND METHODS

Internal residual stresses generated during polymerization of resin composite restorations were determined using micro-photoelastic analysis. Butt-joint preparations simulating Class I restorations (2.0 mm x 5.0 mm, 2.0 mm in depth) were prepared in three types of substrates (bovine teeth, posterior composite resin, and transparent composite resin) and were used to examine contraction stress in and around the preparations. Three types of composite materials (a posterior composite, a self-cured transparent composite, and a light-cured transparent composite) were used as the restorative materials. The self-cured composite is an experimental material, and the others are commercial products. After treatment of the preparation walls with a bonding system, the preparations were bulk-filled with composite. Specimens for photoelastic analysis were prepared by cutting sections perpendicular to the long axis of the preparation. Fringe patterns for directions and magnitudes of stresses were obtained using transmitted and reflected polarized light with polarizing microscopes. Then, the photoelastic analysis was performed to examine stresses in and around the preparations.

RESULTS

When cavity preparations in bovine teeth were filled with light-cured composite, a gap was formed between the dentinal wall and the composite restorative material, resulting in very low stress within the restoration. When cavity preparations in the posterior composite models were filled with either self-cured or light-cured composite, the stress distribution in the two composites was similar, but the magnitude of the stress was greater in the light-cured material. When preparations in the transparent composite models were filled with posterior composite and light-cured transparent composite material, significant stress was generated in the preparation models simulating tooth structure, owing to the contraction of both restorative materials.

CLINICAL SIGNIFICANCE

Polymerization contraction stress is an undesirable and inevitable characteristic of adhesive restorations encountered in clinical dentistry that may compromise restoration success. Clinicians must understand the concept of polymerization contraction stress and realize that the quality of composite resin restorations depends on successful management of these stresses.

Nanoleakage patterns of four dentin bonding systems

OBJECTIVES

The purpose of this study was to evaluate the nanoleakage patterns of four dentin bonding systems.

METHODS

The dentin bonding systems used in this study were: Single Bond, One Coat Bond, Prime & Bond NT/Non Rinse Conditioner (NRC), and PermaQuik. Flat occlusal dentin surfaces from extracted human molars were finished with wet 600-grit silicon carbide paper, and bonded with one of the dentin bonding systems. After 24 h storage at 37 degrees C in water, margins were finished with polishing discs and the surrounding tooth surfaces coated with nail varnish. The samples were immersed in a 50% (w/v) solution of silver nitrate for 24 h, and exposed to photodeveloping solution for 8 h. The samples were cut longitudinally, polished, and mounted on stubs, carbon coated and observed in a Field Emission-SEM using backscattered electron mode.

RESULTS

Different nanoleakage patterns were observed with the different adhesive systems. However, accumulations of silver particles were often noted at the base of the hybrid layer for all materials. Single Bond and One Coat Bond demonstrated uptake of silver particles both within the hybrid layer and the adhesive resin. Prime & Bond NT/NRC showed silver staining throughout almost the entire thickness of the hybrid layer. The leakage pattern of PermaQuik revealed loose silver deposition within the hybrid layer. The composition of each adhesive system may play a role in forming the different leakage patterns.

SIGNIFICANCE

The current dentin bonding systems used in this study do not achieve perfect sealing at the restoration/dentin interface, which may influence the durability of the bond to dentin.

Resin diffusion through demineralized dentin matrix

This paper has focused on the factors that may affect the permeability of adhesive resins into the demineralized dentin matrix during the development of the bonding process. The effects of surface moisture are discussed respectively to the adhesive systems, and the problems related to incomplete hybrid layer formation presented.

Laboratory evaluation and clinical application of a new one-bottle adhesive

PURPOSE

The purposes of this project were to compare the enamel and dentin bond strengths of a new nanofilled one-coat adhesive system with its predecessor, an unfilled two-coat adhesive system; to analyze the dentin interfacial ultramorphology, using scanning and transmission electron microscopy (SEM and TEM); and to illustrate the clinical technique associated with the use of the new nanofilled one-coat adhesive system.

MATERIAL AND METHODS

Twenty flat dentin surfaces and 20 flat enamel surfaces were polished on the labial surface of bovine incisors mounted in acrylic resin. The specimens were equally and randomly assigned to four bonding groups: (1) dentin with Prime & Bond 2.1; (2) dentin with Prime & Bond NT; (3) enamel with Prime & Bond 2.1; and (4) enamel with Prime & Bond NT. A composite post was then adapted to the treated area and light-cured. After thermocycling, shear bond strengths were determined by testing the shear strength of the specimens. The data were analyzed using one-way analysis of variance (ANOVA) and Student's t-test. For SEM and TEM, six dentin disks were obtained from middle dentin of human third molars and assigned equally to each adhesive. The adhesives were applied to dentin according to manufacturer's directions. The hybrid layer and resin penetration into dentin tubules were analyzed at an ultramorphologic level, and the observations were compared.

RESULTS

Shear bond strengths were as follows: group 1: 17.8 +/- 4.1 MPa; group 2: 20.5 +/- 3.5 MPa; group 3: 24.7 +/- 6.7 MPa; and group 4; 27.0 +/- 5.4 MPa. Electron microscopy showed that both adhesives penetrated the dentin tubules and formed a fully infiltrated hybrid layer. The nanofiller included in the new one-application adhesive penetrated the dentin tubules and infiltrated the microspaces between the collagen fibers within the hybrid layer.

CLINICAL SIGNIFICANCE

The new one-application nanofilled adhesive tested in this study resulted in bond strengths and dentin hybridization comparable to those obtained with the corresponding two-application system. The clinical sequences presented illustrate the ease of use of the newest simplified adhesives.

Dentine permeability and tracer tests

OBJECTIVES

This paper reviews the evidence for dentine's permeability in order to clarify and emphasize its confounding effect on leakage test measurements, and hence the need to use special test designs to avoid its effects.

METHODS

The literature on the subject between 1887 and 1997, including 249 articles.

CONCLUSIONS

The prerequisite condition for any tracer penetration test is that unflawed specimens are themselves impermeable to tracer. Entry of tracer then can be used to indicate correctly the location or severity of flaws. The relative impermeability of intact dental enamel permits such testing of the enamel-restoration interface seal, but the same is not true when using dentine, which is usually frankly porous to most tracers through its tubules. False positive results are very likely. Recent intense interest in dentine bonding agents has increased the need and frequency of these tests with dentine, but this serious confounding factor has so far generally remained unstated, and has only been controlled adequately in one study. If tracer penetration test results are to be meaningful, then adequate control is required.

Relation between water content in acetone/alcohol-based primer and interfacial ultrastructure

OBJECTIVES

This study investigated the ultrastructure of the resin-dentine interface when a two-bottle primer system containing NTG-GMA (N(p-tolyl)glycine-glycidyl methacrylate) and BPDM (biphenyl dimethacrylate) was used with different concentrations of water as a part of the primer solvent: (I) an experimental version of All-Bond 2 with no water in primer A; (II) a commercial version of All-Bond 2 (Bisco, Itasca, IL, USA) with 5% water in primer A; and (III) a former version of All-Bond 2 with 17% water in primer A.

METHODS

Thirty-six 1-mm thick dentine discs prepared from third permanent molar teeth were each conditioned with 10% phosphoric acid for 20 s and rinsed for 20 s. They were randomly divided into three groups: Group A, conditioned dentine surface air-dried for 30 s; Group B, air-dried for 3 s; and Group C, blot-dried so that the dentine surface remained visibly moist. The three categories of primers were applied to each disc in 8-10 coats, resulting in nine sub-groups. Discs in each sub-group were bonded together to form disc-pairs using a chemical cure resin, demineralized in ethylene diamine tetraacetic acid (EDTA) and prepared for transmission electron microscopic examination.

RESULTS

With the use of the water-free primer version, sub-optimal hybridization was observed whenever dentine was dried prior to bonding (Groups IA and IB). In the 5% water version, prolonged desiccation resulted in compromised hybridization (Group IIA), while resin globules were observed on the surface of the hybrid layer when a moist technique was employed (Group IIC). In the 17% water version, surface blisters and globules characteristic of the 'overwet phenomenon' were observed in Groups IIIB and IIIC.

CONCLUSION

Between the two extremes of a morphological spectrum of bonding conditions, the different primer versions exhibited different sensitivity ranges. There was a shift in the 'window of opportunity' for optimal hybridization and tubular seal depending on the water content of the primer system investigated.

The dentin substrate: structure and properties related to bonding

OBJECTIVES

Dentin is a vital, hydrated composite material with structural components and properties that vary with location. These variations are reviewed along with alterations by physiological and pathological changes that allow classification into various forms of dentin. Structural characteristics and mechanical properties are reviewed and the limitations of our understanding of structure-property relationships for normal and modified forms of dentin are discussed with respect to their impact on dentin bonding. Recent progress in methods available to study dentin and its demineralization are emphasized with their promise to increase our understanding of dentin properties and structure.

DATA SOURCES

Recent microstructural studies, focusing on scanning electron microscopy, atomic force microscopy and X-ray tomographic microscopy are included. A review of fundamental studies with emphasis on microstructurally sensitive methods, and prior reviews of basic mechanical properties are included with discussion of their correlation to composition and structure.

STUDY SELECTION AND CONCLUSIONS

Emphasis in this work was placed on the major structural components of the tissue, including the collagen based organic matrix and its mineral reinforcement, the distribution of these components and their microstructural organization as related to mechanical properties and response to demineralization. Little information is included on biochemical and developmental studies or on non-collagenous proteins and other organic components for which limited understanding is available with respect to their role in structure-property relations and influence on bonding. In spite of the fact that the complexity of dentin precluded a comprehensive review, it is clear that local structural variations influence properties and impact nearly all preventive and restorative dental treatments. Much more work is needed in order to understand differences between vital and non-vital dentin, and dentin from extracted teeth. Although our knowledge is rudimentary in certain areas, increasingly sophisticated methods of studying dentin should provide the necessary information to model structure-property relations, optimize dentin bonding, and improve many aspects of preventive and restorative dentistry.

Dentine permeability and dentine adhesion

OBJECTIVES

The objectives of this paper are to review the structure of dentine as it pertains to adhesive bonding and to describe the importance of resin permeation into dentinal tubules and into spaces created between collagen fibrils by acid-etching during resin bonding. The advantages and disadvantages of separate acid-etching, priming and adhesive applications are discussed.

DATA SOURCES

Although not an exhaustive review, the concepts included in the review were obtained from the dentine bonding literature.

STUDY SELECTION

Attempts were made to critically evaluate what is known about dentine permeability and adhesion and what remains to be discovered. Speculations were made on a number of controversial issues that are not yet resolved.

CONCLUSIONS

Acid-etching of dentine produces profound changes in the chemical composition and physical properties of the matrix which can influence the quality of resin-dentine bonds, their strength and perhaps their durability.

Mapping of tubule and intertubule surface areas available for bonding in Class V and Class II preparations

OBJECTIVES AND METHODS

The aim of this in vitro study was to evaluate the morphology of dentine in Class V and the Class II preparation walls in terms of tubule orientation, density and increase in surface area after conditioning. Six circular V-shaped preparations were cut at the cementum-enamel junction (CEJ) of anterior teeth and six Class II cavities with the cervical margin 1 mm below the CEJ were prepared in posterior teeth. The preparations were conditioned with 10% maleic acid. The samples were directly studied by SEM. The observations were organized according to location in the preparation, tubule density was counted and the increase in area available for bonding after acid etching was calculated.

RESULTS

Dentine morphology of Class V and Class II preparation walls was mostly regular according to predictable patterns. Between the tubules, along the walls of the cavity, the etched dentine surface exhibited a porous network of collagen fibers. More than 50% of Class V and Class II cavity surface presented oblique or parallel tubule orientation with respect to the cut surface. Because of the presence of a structureless cementum layer. the morphology of the cervical area turned out to be less predictable. The tubule density varied considerably in different regions of the preparations. The intertubular dentine surface area increased after conditioning in Class V preparations from 20.9% to 50.3% on the walls where tubules were cut parallel to their long axis, and from 5.8% to 47.8% where tubules were cut perpendicularly. These same values for Class II preparations ranged from 0.6% to 46.4% on the walls where tubules were cut parallel to their long axis, and 29.8% of the tubules were cut perpendicularly.

CONCLUSIONS

Based on this morphological investigation, the increase in intertubular dentine surface area might very well be responsible for the enhanced bond strength after acid etching of dentine, but not all areas exhibited equal responses to etching. In particular, the bonding substrate at the gingival margins may contribute little in terms of micromechanical retention.

The overwet phenomenon in two-component acetone-based primers containing aryl amine and carboxylic acid monomers

OBJECTIVES

The overwet phenomenon was first reported when a moist bonding technique was used with an earlier commercial version of All-Bond 2 (Bisco) that contained BPDM in primer B. This study investigated whether ultrastructural features of the overwet phenomenon could also be detected in other commercially available two-component acetone-based primers containing BPDM, PMDM and PMGDM, as well as an experimental two-component primer containing DSDM.

METHODS

Thirty 1 mm dentin discs prepared from third molars were each conditioned with 10% H3PO4 for 20 s and rinsed for 20 s. They were randomly divided into 5 groups: Group I (Bond-It, Jeneric/Pentron:PMGDM); Group II (Wet Bond, Chameleon Dental Products:PMGDM); Group III (Tenure S, Den-Mat:PMDM); Group IV (present commercial version of All-Bond 2, Bisco:BPDM) and Group V (Experimental two-component primer system containing DSDM in primer B). Following a moist bonding technique using the respective system, discs from each group were further bonded together to form three disc pairs using a chemical-cured resin. Bonded disc pairs were demineralized in EDTA and processed for TEM examination. For this ultramicroscopical study, results such as the features of the overwet phenomenon were analyzed by visual inspection of the specimens in each group (n = 12).

RESULTS

Isolated blister-like spaces of variable dimensions were observed within the primer layer in all groups and possessed the following characteristics: 1) a layer of resin-impregnated dentin was always present along the base of the primary blister; 2) surface primer globules, sometimes containing secondary blisters, were identified within these primary blisters; 3) dentinal tubules within the blister-like spaces were not completely sealed; 4) primer globules were circumscribed by a halo of fine kinked strands of material.

SIGNIFICANCE

Although the technique of moist bonding is based on valid biological principles, incorporation of resin monomers that are immiscible with water rendered the application of current two-component, acetone-based primers very technique-sensitive in terms of tubular seal, when used on moist, acid-conditioned dentin. Further studies should be directed at elimination of this type of oil-in-water (O/W) "macroemulsion" formation through optimal micellar solubilization of these resin monomers in water.

Current concepts on adhesion to dentin

This review examines fundamental concepts in bonding to dentin. Emphasis is placed on the structure and permeability characteristics of dentin and how they may influence its interaction with adhesive resin. Several new techniques to examine the interfaces between resin and dentin are reviewed along with some of their limitations. The advantages and disadvantages of acid etchants/conditioners vs. self-etching conditioners/primers are discussed. The problems of matching the surface tension of resin-bonding systems to the surface energy of the substrate are reviewed in terms of wetting the various components of dentin. The problems associated with matching the permeability of intertubular dentin to the diffusibility of bonding reagents are explored. Speculation is advanced on how to ensure polymerization and wetting of dentinal collagen. Theoretical problems associated with dentin bonding and with bond testing are reviewed to encourage future research in this rapidly developing area.

Micromorphological spectrum from overdrying to overwetting acid-conditioned dentin in water-free acetone-based, single-bottle primer/adhesives

OBJECTIVES

The goal of this study was to illustrate and define the micromorphological spectrum which exists at the resin-dentin interface when two water-free, acetone-based, single-bottle primer/adhesive systems (One-Step, Bisco, and Prime & Bond, Dentsply/L.D. Caulk) were applied to acid-conditioned dentin under different dry and wet bonding conditions.

METHODS

Forty-eight 1 mm dentin discs were each conditioned with 10% phosphoric acid and rinsed for 20 s. They were randomly divided into 4 groups based upon the status of the remaining surface moisture; Group I (30 s dry); Group II (3 s dry); Group III (blot dry) and Group IV (overwet). Bonded dentin disc pairs were then demineralized in EDTA and embedded in epoxy resin for transmission electron microscopic examination.

RESULTS

The micromorphological spectra of the two bonding systems were essentially similar. Both were effected by even mild desiccation (3 s), resulting in incomplete intertubular resin infiltration. Optimal intertubular resin infiltration was achieved when the collagen network was kept moist and appeared relatively unaffected by the presence of excess surface moisture. On the other hand, intratubular resin infiltration was severely compromised in the presence of excess water within the dentinal tubules and at their openings in the dentin surface. The continuity of the resin layer deteriorated; blister-like spaces formed on the dentin surface and resin globules were found around the tubular orifices and on the surface of the hybrid layer. In addition, a complex phase separation pattern was observed in Prime & Bond that was characterized by phase inversion in the presence of surface moisture.

SIGNIFICANCE

The "window of opportunity" for optimal interfacial integrity for both water-free systems appeared to depend upon keeping the demineralized collagen network moist, coupled with the complete evaporation of excess and "displaced" water from tissues prior to light-curing the prime/adhesives.

Resin permeation into acid-conditioned, moist, and dry dentin: a paradigm using water-free adhesive primers

Preservation of the morphological integrity of demineralized dentin collagen in its hydrated state may account for the success observed in wet-bonding procedures. This study investigated the micromorphological differences between moist- and dry-bonding techniques with the use of: (a) Aelitebond, an alcohol-based, water-free, single-component dentin adhesive primer system; and (b) a water-free, acetone-based experimental primer similar to the acetone-based, water-containing All-Bond 2, a two-component primer system. In the wet groups, acid-conditioned dentin surfaces were blotted so that they remained visibly moist prior to bonding. In the dry groups, dentin surfaces were air-dried for 30 sec. Following the bonding procedures, dentin discs in each group were laminated together by means of a chemical-cure resin and processed for scanning electron microscope (SEM) and transmission electron microscope (TEM) examination. Conditioning with 10% H3PO4 for 20 sec. produced complete demineralization of the outer dentin. In the wet groups, banded collagen and interfibrillar spaces could be observed at the surface of the acid-conditioned dentin. Complete wetting of the loosely arranged collagen fibrils by the resin resulted in the formation of a hybrid layer. In the dry groups, only a very thin hybrid layer was observed on the dentin surface, along the walls of the tubules, and along the course of their lateral branches. The absence of banded collagen and interfibrillar spaces within these areas suggested the existence of a collapsed dentin matrix along various liquid-vapor boundaries that restricted resin permeation into the subsurface intertubular matrix, producing an incompletely infiltrated "hybridoid region".